How Does The Calorie Calculator Work?
If you’ve seen the latest diet tools on this site, you’ve no doubt noticed the button where you can click to calculate your calorie needs. (“Calorie Calculator” box under the “Diet Tools” tab). Really all you have to do is insert your height, weight, gender, age, and activity level, and the tool actually does all the calculating for you! But how do they arrive at this number, is it reliable, and what are the advanced tools?
You’ll find that when you plug in your data you can click the “advanced options” button and see three different methods that can be used to calculate your calorie needs. The first one you see is the Mifflin-St Jeor equation and the third is the Harris-Benedict equation. Both are formulas derived to measure how many calories you burn, as accurately as possible, using your height, weight, age, and gender.
In reality, the best way to measure the number of calories you burn is to get hooked up to a machine called an Indirect Calorimeter. This machine measures the oxygen you breathe in and the carbon dioxide you breathe out, and then calculates the number of calories you are burning based on those figures. Researchers use groups of individuals, calculate their actual calories burned as closely as possible, and then work up calculations to determine as closely as possible what constants we can use to come up with comparable numbers. Harris and Benedict derived their formula in the early 1900′s and it was virtually the only one in use by clinical nutritionists until the 1990′s. Today many researchers believe that one of the new standard formulas–the Mifflin-St.Jeor equation–more accurately reflects how many calories we burn based on changes in our body composition since the last hundred years have passed.
The equations are as accurate as they can be given the information we put in. When I plugged in my information I got two very different numbers for each of the options: 1613 calories for the MSJ option, and 1783 calories for the H-B. Harris-Benedict tends to overestimate and obviously it’s the number I would choose if I could… but it’s not up to me!
And it’s also not an exact science. Two people who are the same height, weight, and age will always burn a different number of calories in reality. Many other factors will affect how many calories burned during the day, not the least of which is activity level. Body composition also matters, and the second option under ‘advanced’ is using your body fat percentage to find how many calories you burn in a day. Next week I’ll tell you how you can measure your body fat percentage.
Written by Laurie Beebe
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About The Author: Laurie Beebe has been a registered dietitian for 25 years and is certified in adult weight management. Laurie currently serves as a Related posts:
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